The present disclosure relates to aircraft environmental control systems. More specifically, the present disclosure relates to a second stage turbine nozzle for an air cycle machine.
Air cycle machines are used in environmental control systems in aircraft to condition air for delivery to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressured air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the air cycle machine before the air is delivered to the aircraft cabin.
Air cycle machines typically utilize turbine nozzles that can rotate to direct air in a radial direction with respect to a main axis of the air cycle machine. Turbine nozzles are typically coated with an erosion coating to protect the turbine nozzles from damage. Erosion can be caused by particles in the air flowing through the air cycle machine. Applying a coating to the turbine nozzle will cause the coating to erode but will protect the turbine nozzle from erosion. The coating can be reapplied as needed to fill areas that have eroded to extend the life of the turbine nozzle in the air cycle machine.
Turbine nozzles are typically cast, so prior to applying a coating, turbine nozzles have to be post-processed to smooth the turbine nozzle. Post-processing can include machining or sand blasting. The coating can be applied using a number of different thermal spraying techniques, including detonation gun spraying and high velocity oxygen fuel (HVOF) spraying. Detonation gun spraying applies a coating using a detonation gun with a long water-cooled barrel. Oxygen, fuel, and powder are fed into the barrel of the detonation gun and a spark is used to ignite the oxygen and fuel mixture. This will heat the powder and accelerate the powder through and out of the barrel to be applied to a substrate. HVOF spraying applies a coating using a combustion chamber. A mixture of fuel and oxygen is fed into the combustion chamber where it is ignited and combusted continuously. The hot gas from the combustion will travel through a nozzle and a powder feed stock is fed into the gas stream in the nozzle. The powder feed stock will partially melt and will flow out of the nozzle to be deposited on a substrate.